A light emitting device using a light emitting diode (LED) is made generally of a combination of an LED chip as an excitation light source and a phosphor excited by the excitation light. Light with various colors can be realized by changing the combination.
A white light emitting device emitting white light uses a combination of a blue LED emitting blue light and a phosphor, for example. In a white light emitting device, a blue LED having a peak wavelength around 460 nm is generally used to realize high excitation efficiency of a phosphor.
On the other hand, light around 460 nm accelerates a secretion of melatonin from a human body. Therefore, it is concerned that use of the white light emitting device may alter a biological rhythm.